Circulating fluidized bed boiler with bottom-supported in-bed heat exchanger

Abstract

A circulating fluidized bed (CFB) boiler has one or more bubbling fluidized bed enclosures containing heating surfaces and located within a lower portion of the CFB boiler to provide an in-bed heat exchanger (IBHX). Solids in the bubbling fluidized bed are maintained in a slow bubbling fluidized bed state by separately controlled fluidization gas supplies. The beds feature open bottom distribution grids with hoppers disposed below to collect solids. The enclosure defining the IBHX is supported from structures below the grids and the enclosure can be supported from the hoppers.

We claim: 
     
         1 . A circulating fluidized bed (CFB) boiler comprising:
 a CFB reaction chamber having side walls and an open-bottom grid defining a floor at a lower end of the CFB reaction chamber for providing fluidizing gas into the CFB reaction chamber;   at least one bubbling fluidized bed (BFB) located within a lower portion of the CFB reaction chamber and being bound by enclosure walls and the floor of the CFB reaction chamber, with the fluidizing gas feed to the BFB portion of the grid controlled separately from the fluidizing gas feed to the CFB portion of the grid;   at least one controllable in-bed heat exchanger (IBHX), the IBHX occupying part of the CFB reaction chamber floor and being surrounded by the enclosure walls of the BFB;   bottom-supported hoppers containing dormant solids disposed under the CFB and the BFB;   the enclosure walls of the BFB being supported off the bottom-supported hoppers;   the enclosure walls of the BFB are of cooled membrane gas-tight design around the perimeter of the BFB, including:   at least one top opening for CFB solids influx into the BFB;   at least one overflow port for setting the BFB height;   at least one underflow port for BFB solids controlled recycle back into the CFB;   the gas-tight BFB enclosure extending below the grid to the elevation sufficient for not exceeding a preset percentage of leakage of the fluidizing gas from the BFB into the CFB through the bed of the dormant solids between the aforementioned elevation and the grid; and   the tubes of the BFB enclosure below that elevation becoming of a loose design with sufficient flexibility for accommodating differences in thermal expansion of the tubes and the hoppers as the tubes penetrate the walls of the hoppers.   
     
     
         2 . The CFB boiler according to  claim 1 , wherein the walls of the CFB reaction chamber are top supported and an expansion joint is installed around the perimeter of the reaction chamber between its walls and the hoppers for providing a pressure seal while allowing the downward expansion of the walls and the upward expansion of the hoppers. 
     
     
         3 . The CFB boiler according to  claim 1 , wherein the BFB enclosure includes a secondary gas duct. 
     
     
         4 . The CFB boiler according to  claim 3 , wherein the secondary gas duct is made of tubes of the BFB enclosure. 
     
     
         5 . The CFB boiler according to  claim 3 , wherein the secondary gas duct is supplied with the secondary gas through at least one conduit made of membrane panels extending downward to essentially the same elevation as where the gas-tight BFB enclosure terminates and turns into a loose-tube design. 
     
     
         6 . The CFB boiler according to  claim 5 , wherein the at least one secondary gas conduit upon termination of the membrane-panel design:
 continues as a plate-type design gas-tightly connected to the membrane-panel part of the conduit, the connection design allowing an independent thermal expansion of either part,   the plate-type part further penetrating through the hopper wall, the penetration design accommodating independent thermal expansions of the conduit and the hopper, and   the tubes forming the membrane-type part becoming of a loose design with sufficient flexibility for accommodating differences in thermal expansion of the tubes and the hopper as the tubes penetrate the hopper wall.   
     
     
         7 . The CFB boiler according to  claim 1 , wherein the walls of the CFB reaction chamber are bottom supported. 
     
     
         8 . A circulating fluidized bed (CFB) boiler comprising:
 a CFB reaction chamber having walls and an open-bottom grid defining a floor at a lower end of the CFB reaction chamber for providing fluidizing gas into the CFB reaction chamber;   at least one bubbling fluidized bed (BFB) located within a lower portion of the CFB reaction chamber and being bound by enclosure walls and the floor of the CFB reaction chamber, with the fluidizing gas feed to the BFB portion of the grid controlled separately from the fluidizing gas feed to the CFB portion of the grid;   at least one controllable in-bed heat exchanger (IBHX), the IBHX occupying part of the CFB reaction chamber floor and being surrounded by the enclosure walls of the BFB;   hoppers containing dormant solids disposed under the CFB and the BFB; and   the enclosure walls of the BFB being supported off the bottom-supported hoppers.   
     
     
         9 . The CFB boiler of  claim 8 , wherein the hoppers include an inner hopper for the BFB and an outer hopper for the CFB; a skirt connected to a portion of the enclosure walls and extending into the inner hopper to form a seal. 
     
     
         10 . The CFB boiler of  claim 8 , further comprising thermal expansion accommodating support plates supporting the enclosure walls from the bottom-supported hoppers. 
     
     
         11 . The CFB boiler of  claim 10 , wherein the enclosure walls include membranes; the support plates being connected to the membranes. 
     
     
         12 . The CFB boiler of  claim 11 , wherein the membranes terminate below the connection of the support plates and the membranes. 
     
     
         13 . The CFB boiler of  claim 8 , wherein the walls of the CFB reaction chamber are top supported and an expansion joint is disposed around the perimeter of the CFB reaction chamber between its walls and the hoppers for providing a pressure seal while allowing the downward expansion of the walls and the upward expansion of the hoppers. 
     
     
         14 . The CFB boiler of  claim 8 , wherein the enclosure walls of the BFB are of cooled membrane gas-tight design. 
     
     
         15 . The CFB boiler of  claim 14 , wherein the BFB enclosure includes a secondary gas duct. 
     
     
         16 . The CFB boiler of  claim 15 , wherein the secondary gas duct is made of portions of the BFB enclosure walls. 
     
     
         17 . The CFB boiler of  claim 15 , wherein the secondary gas duct is supplied with the secondary gas through at least one conduit made of membrane panels extending downward to about the same elevation as where the BFB enclosure is supported by the hoppers. 
     
     
         18 . The CFB boiler of  claim 17 , wherein the at least one secondary gas conduit, below the same elevation:
 continues as a plate-type design gas-tightly connected to the membrane-panel part of the conduit, the connection design allowing an independent thermal expansion of either part;   the plate-type part further penetrating through the hopper wall, the penetration design accommodating independent thermal expansions of the conduit and the hopper; and   the tubes forming the membrane-type part becoming of a loose design with sufficient flexibility for accommodating differences in thermal expansion of the tubes and the hopper as the tubes penetrate the hopper wall.   
     
     
         19 . A circulating fluidized bed (CFB) boiler comprising:
 a CFB reaction chamber having walls and an open-bottom grid defining a floor at a lower end of the CFB reaction chamber for providing fluidizing gas into the CFB reaction chamber;   at least one bubbling fluidized bed (BFB) located within a lower portion of the CFB reaction chamber and being bound by enclosure walls and the floor of the CFB reaction chamber, with the fluidizing gas feed to the BFB portion of the grid controlled separately from the fluidizing gas feed to the CFB portion of the grid;   the enclosure walls of the BFB are of cooled membrane gas-tight design;   at least one controllable in-bed heat exchanger (IBHX), the IBHX occupying part of the CFB reaction chamber floor and being surrounded by the enclosure walls of the BFB;   hoppers containing dormant solids disposed under the CFB and the BFB; and   the enclosure walls of the BFB being connected to at least one of the bottom-supported hoppers with supports and becoming of a loose design with sufficient flexibility for accommodating differences in thermal expansion of the tubes and the hopper as the tubes penetrate the hopper wall.